Nickel Felt vs Titanium Felt: Which Substrate Fits Your Stack?
Nickel felt and titanium felt share the same architecture — metal fibers sintered into a porous, conductive, compressible sheet. What separates them is chemistry, and chemistry is not negotiable inside an electrolyzer. This guide compares the two on corrosion behavior, electrical performance, mechanics and cost, and ends with a decision rule you can apply to a stack drawing in five minutes.
The chemistry decides, everything else follows
In KOH, nickel forms a thin, stable hydroxide layer that is itself conductive. That makes nickel felt the default electrode substrate and porous transport layer for alkaline and AEM stacks: it survives decades of caustic service, it is inexpensive relative to titanium, and it accepts catalytic coatings (Raney Ni, NiFe) well. Put the same felt into a PEM anode and the story inverts: nickel dissolves in hot concentrated acid under oxygen evolution, and the dissolved ions migrate into the membrane.
Titanium’s protective TiO&sub2; skin makes it one of very few metals that endure the acidic, oxygen-evolving PEM anode. But that same skin is electrically insulating and thickens under anodic potential, which is why commercial Ti felt for electrolysis is supplied with a thin platinum coating (0.2–0.5 μm): the coating keeps the fiber-to-catalyst contact resistance low for the life of the stack.
Side by side
| Property | Nickel fiber felt | Titanium fiber felt |
|---|---|---|
| Corrosion environment | Alkaline (KOH), neutral | Acidic and oxidizing, alkaline, chlorine-free brines |
| Natural stack position | ALK/AEM electrode substrate, PTL, current collector | PEM anode PTL; AEM anode where margin is wanted |
| Surface conductivity | Conductive oxide layer (no coating needed) | Insulating TiO&sub2; — Pt coating required for stable contact |
| Thickness range (commercial) | 0.2–1.0 mm (composite up to 1.5 mm) | 0.2–1.0 mm |
| Porosity range (commercial) | 50–80% | 50–70% (graded porosity available) |
| Typical pore size | 18–60 μm | 18–50 μm (MPL structures 100–200 μm optional) |
| Areal resistance | Low, continuous fiber network | ≤5 mΩ·cm² with Pt coating (published product spec) |
| Cathode-side caveat | Stable in alkaline | Hydriding risk at strongly cathodic potentials — review before use |
| Cost logic | Reference material | Several times nickel; Pt coating adds cost |
| Max sheet size (our production) | 800×1500 mm | 800×1500 mm |
Mechanics: felt behaves differently from mesh or foam
A sintered fiber felt compresses slightly and evenly, which is exactly what a stack needs to close microscopic gaps between the bipolar plate and the catalyst layer. Mesh is stiffer but touches at wire crossings only; foam has enormous porosity but little strength. In practice:
- At the PEM anode, Ti felt’s combination of compliance and uniform porosity is why it displaced perforated plates in most megawatt-class designs; rigid porous Ti plates come back where flatness and fine pores matter more than compliance.
- At large alkaline/AEM areas, a single felt sheet sags; mesh-reinforced nickel felt (felt co-sintered onto an expanded Ni mesh) carries the conductivity and the mechanical load together.
- Nickel foam suits catalyst-loading roles, not high-compression PTL roles — pressed too hard, its pore walls collapse.
The cost argument, done properly
Titanium felt costs several times nickel felt per square meter, and Pt coating adds more. The correct comparison is not price per sheet but cost per cell over stack life: in a PEM anode, titanium is not an upgrade over nickel — it is the only material that survives, so the comparison is Ti felt versus failure. Conversely, specifying Ti felt inside an alkaline stack buys corrosion margin nobody needs and pays for it on every square meter.
Decision rule
- Acidic (PEM) anode → Pt-coated Ti felt or porous Ti plate. See titanium felt for hydrogen production and porous titanium plate.
- Alkaline or AEM → nickel felt, reinforced with mesh for large areas. See nickel fiber felt and mesh-reinforced nickel felt.
- Uncertain about the local potential or electrolyte? Send the stack drawing and operating window — a one-page review usually settles the material within a day.
Frequently asked
Can nickel felt be used in a PEM electrolyzer?
No. Hot acidic electrolyte with oxygen evolution dissolves nickel, and dissolved nickel contaminates the membrane. Nickel felt is the standard for alkaline and AEM stacks instead.
Can titanium felt be used in an alkaline electrolyzer?
Chemically it tolerates caustic solution, but nothing in an alkaline stack requires it — nickel performs the same function at a fraction of the cost, so commercial alkaline stacks use nickel hardware.
How thick should the platinum coating be?
Commercial specifications commonly land at 0.2–0.5 μm. The coating stabilizes contact resistance; beyond that range, thickness adds cost without proportional benefit.
Is titanium felt safe on the cathode side?
Only after a hydriding review: titanium absorbs hydrogen at strongly cathodic potentials and can embrittle. Most PEM designs keep carbon-based layers on the cathode.
How are Pt / Ir coatings applied and verified? See the dedicated guide: Platinum or Iridium? Coating Processes for Titanium PTLs.
Need a material quote for your stack?
AIFILTECH sinter-manufactures the porous metal layers that go between the bipolar plate and the catalyst: titanium fiber felt (with optional Pt coating 0.2–0.5 μm), porous titanium plates, nickel fiber felt, mesh-reinforced nickel felt, nickel mesh and multi-layer sintered mesh.
- Send us: stack type (PEM / alkaline / AEM), active area per cell, target thickness, porosity, coating requirement and annual volume.
- You get: a specification confirmation within one business day, sample sheets for stack trials, and consistent batch data.